OBJECTIVE: To develop a cheap, rapid, comprehensive and biologically relevant bioassay for screening the antitumor activity of reticuloendothelial stimulants in vivo. APPROACH: To measure the extent of clearance of intravenously injected radiolabeled tumor cells from the lungs following prior immunoprophylaxis with reticuloendothelial stimulants. CURRENT PROGRESS: To date the optimum doses, time for initiation of the effects, magnitude of effects, and duration of effects have been established in a comparative fashion for BCG, glucan, and C. parvum, in the TS1699 DBA2 mouse mammary carcinoma and the B16C57B16J mouse melanoma. Those obtained with the B16 tumor correlate to a high degree with differences observed in the outgrowth of lung tumor nodules. Initial studies with differences observed in the outgrowth of lung tumor nodules. Initial studies with coded samples of developmental analogues of MDP's and a series of glucans have shown preliminary promise in separating those compounds with superior antitumor activity.